Japan: no evidence ANA 787 battery was overcharged

TOKYO--Japanese aviation officials said Wednesday that flight data from a Boeing Co.
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Dreamliner jet that made an emergency landing in central Japan last week has shown no evidence so far that the battery was overcharged, a finding that sheds a new light onto what went wrong on the flight.

Norihiro Goto, the chairman of the Japan Transport Safety Board, told reporters at a press conference that data acquired from the Dreamliner's digital flight data recorder showed there was nothing "abnormal" in the battery's voltage level before a series of alarms went off in the plane's cockpit. The pilots of the plane, operated by All Nippon Airways Co. (9202.TO), decided to make an emergency landing because of a smoldering smell emanating from the electrical compartment below the deck where the highly flammable lithium-ion battery was installed.

The latest finding potentially changes the direction of the Japanese investigation into what went wrong with the plane and brings it more in line with what U.S. investigators have found in a similar incident in Boston. In that incident, a battery on a parked Dreamliner operated by Japan Airlines Co. (9201.TO) caught fire.

The U.S. National Transportation Safety Board said earlier this week that the JAL 787's battery "did not exceed its designed voltage." One of the Japanese investigators looking into the ANA Dreamliner incident said last week that the burn marks on the charred battery suggested overcharging, as among the more likely causes initially leading to the impression that the U.S. and Japanese probes were headed in different directions. Data from the aircraft's digital flight data recorder was not available at the time.

The twists and turns of the U.S and Japan probes -- run separately but with the cooperation of the other -- underscore the difficulty of troubleshooting the advanced electrical system that powers Boeing's flagship jet, celebrated at its launch for its revolutionary features. Among them is the Dreamliner's heavy reliance on electrical systems to perform many functions that were previously handled mechanically. The plane, for instance, moves parts of wings electrically instead of with hydraulic devices.

Two engineers from Thales S.A. (HO.FR) of France joined the investigative team in Japan on Tuesday, transport ministry officials said Wednesday. Thales designs and makes electrical systems for the aerospace and transport industries--including the battery-operation system for the Boeing
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787. Engineers with GS Yuasa Corp. (6674.TO), the maker of the 787's lithium-ion batteries, are also involved of the investigation.

The U.S. Federal Aviation Administration and other global aviation regulators last week grounded all Dreamliners until regulators are convinced the battery systems are safe.

The data found on the digital flight data recorder of the ANA Dreamliner showed that the output voltage of the battery did not exceed the maximum 32 volts, said Mr. Goto of the JTSB on Wednesday. It had stayed at 31 volts before suddenly dropping and then moving up and down, indicating that overcharging may not have been the cause of the incident.

But JTSB officials cautioned that there is still insufficient data to rule out any potential causes of the incident entirely, since it's still unclear whether the voltage fluctuations were a cause or symptom of the problems.

One unknown is whether there was excess voltage coming into the battery, said Mr. Goto. The data showed only the voltage of the battery output, not inflow of electricity into the battery, he said.

The JTSB will also have to investigate the battery charger to figure out whether there may have been overcharging from the charger, Masahiro Kudo, a director general of the JTSB told reporters after the press conference.

The flight data also suggested that the battery wasn't used during the flight. Instead, power was supplied by four generators connected to the engines. The voltage level remained stable throughout the flight until the alarms went off.

Mr. Goto said the next step of the investigation will be to figure out why the voltage suddenly dropped.

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